Back pain resulting from degenerative disc disease is a major cause of morbidity, disability, and lost productivity. Back pain is the most frequent cause of activity limitation in people under the age of 45, the second most frequent reason for physician visits, the fifth-ranking reason for hospitalization, and the third most common reason for surgical procedures. Additionally, chronic back conditions that are both common and debilitating occur in 15 to 45 percent of people each year, and in 70 to 85 percent of people at some time in their lives. The financial impact in terms of health care dollars and lost work hours to society is between $20 billion and $50 billion per year in the United States alone.
Despite the continued improvements in non-operative and operative treatment options for patients with lower back pain secondary to degenerative disc disease, no treatment modalities have served as the “magic bullet” to eliminate or consistently improve this condition. Today, however, there are new and exciting opportunities for the development of treatment modalities derived from the merging of biomedical engineering and molecular science. We are closer today then ever before to creating new treatment modalities and devices for the treatment of degenerative disc disease. Recent examples of advancements in bioscience and the effect on clinical spine disease include the development of fusion proteins, total disc arthroplasty and more recently nucleus arthroplasty. Fusion proteins, such as recombinant human bone morphogenetic protein-2 (rhBMP-2), are genetically produced proteins that have the ability to stimulate new bone growth to allow for a more reliable and rapid fusion of spinal vertebrae in the context of surgical reconstruction.
The first total disc arthroplasty was performed by Fernstorm in the late 1950's. Although initially there was a short period of symptom relief, the prosthesis ultimately failed secondary to subsidence of the implant within the spine verebra. Although total disc arthroplasty for the lumbar spine has been performed in Europe since the late 1980's, its use in the United States did not begin until March of 2000 with the introduction of the SB Charité III (DePuy Spine, Raynham, Mass.). 10,11 Several other lumbar spine prostheses have since been introduced, including the Maverick (Medtronic Sofamor Danek, Memphis, Tenn.), the ProDisc-L (Spine Solutions/Synthes, Paoli, Pa.), and FlexiCore (Stryker Spine, Allendale, N.J.). Each of these prostheses differs in design with respect to bearing surface, fixation to bone, number of articulations, material, constraint, and mobility of the center of rotation. In addition to the lumbar disc arthroplasty, as of last year trials for cervical disc arthroplasty have begun in the United States. Models of cervical disc arthroplasty include the Bryan Cervical Disk (Medtronic Sofamor Danek), the Prestige ST (Medtronic Sofamor Danek), the Porous Coated Motion artificial cervical disk (Cervitech, Rockaway, N.J.), and the ProDisc-C (Spine Solutions/Synthes).
Nucleus arthroplasty or nucleus replacement devices for degenerative spine disease such as the PDN® Prosthetic Disc Nucleus are similar in concept to TDA and have shown successful results. The PDN® device consists of a hydrogel core center encased in a polyethylene sleeve which shrinks and swells during normal loading and unloading allowing for restoration of disc space height and thus mimicking healthy human disc.
Although the total disc arthroplasty and nucleoplasty may serve as an alternative to interbody spinal fusion, the procedure is not without its complications. The most common complications include adjacent level spinal disease, subsidence, and facet joint arthrosis. Furthermore, recent studies from clinical trials have demonstrated incidences of infection, vertebral body fracture, implant malposition, subsidence, mechanical failure, and paravertebral heterotopic ossification. More serious complications, including anterior dislocation of the implant, have been reported. Also, the issue of wear particles from the total disc arthroplasty (TDA) and the potential effects on the spinal cord are still not known. It is therefore evident that although the development of the total disc arthroplasty is a step forward in the treatment of degenerative disc disease, the ultimate goal should be the development and replacement of a degenerative disc with a new biologic disc which does not have the complications associated with mechanical parts.
More than one million spine surgery procedures are performed annually in United States. Furthermore, the lumbar fusion segment of the spine surgery market is estimated at well over $1 billion in annual revenue.